This proposal outlines an experimental investigation of a series of structurally-related, hydrophobic peptides which are known to increase the permeability of cell membranes and lipid bilayers. It is directed to understanding the role that proteins play in membrane transport processes. The goals of this research are threefold: (1) to provide quantitative descriptions of the 3-dimensional structures and shapes of these molecules; (2) to learn how their biological activity and conformation are related to their primary (covalent) structure; (3) to describe the molecular mechanisms of membrane-transport processes. To accomplish these goals, conformational properties, as well as equilibrium and kinetic data on cation-peptide interactions will be determined as functions of the primary (covalent) structure of the peptide: (2) the size and charge of the interacting cations; (3) environmental factors such as those determined by the solvent and temperature. Nuclear magnetic resonance (NMR) techniques are the principal methods used in these studies. Results from experiments involving double resonance, relaxation studies as well as spectral and band-shape analysis will be combined to provide quantitative information about proton-proton distances, bond dihedral angles, the location of intramolecular H-bonds and kinetic data concerning conformational fluctuations, molecular tumbling and cation-peptide interactions.